Thin Film Transistor TFTs with a compound semiconductor (the representative of which is metal oxide) as the material of an active layer have the merits of high mobility, simple manufacturing process, good large-area homogeneity, low manufacturing cost, etc., and are regarded as the most promising devices for driving Active Matrix Organic Light Emitting Diode (AMOLED) to display. Therefore, compound semiconductor TFTs attract a lot of attentions of the industry in recent years, and are gradually applied to AMOLED display panels.
In the manufacturing technology of TFTs, the Back Channel Etch (BCE) process is a common process for amorphous silicon TFTs, and TFTs can be formed by only four photolithographic processes. A gate electrode of a TFT is formed by the first photolithographic process, a semiconductor layer of the TFT is formed by the second photolithographic process, a source electrode and a drain electrode of the TFT are formed by the third photolithographic process, and a passivation-layer via hole of the TFT is formed by the fourth photolithographic process. The BCE process is widely adopted by an existing amorphous silicon (a-Si) TFT panel production line because it needs smaller mask number (four masks) and fewer process steps. Taking metal oxide TFTs as examples, theoretically, the manufacturing process of compound semiconductor TFTs should be the same as that of amorphous silicon TFTs. But whether a dry etching or a wet etching will cause damage to a compound semiconductor active layer possessing a relatively vulnerable chemical stability, and thus the device performance is affected ultimately. Namely, with the BCE process, the compound semiconductor active layer will be damaged simultaneous with the formation of a source electrode and a drain electrode. Therefore, the BCE process cannot be directly used to manufacture a compound semiconductor thin film transistor, and it is necessary to add a manufacturing process of an etch barrier layer useful for protecting a compound semiconductor active layer. However, after the etch barrier layer is added, the mask number necessary for the manufacturing process is increased consequently, and the process becomes complicated and the cost is increased accordingly.